1. Field of the Invention
This invention relates to cooling arrangements for high output engines, and more specifically to a wet/dry cylinder liner for such engines.
2. Description of the Prior Art
There has been a trend to increase the output of internal combustion engines by increasing the firing pressures and thermal loading of such engines. This trend has tended to favor the adoption of wet-type liners in the cylinder block where the liner is in direct contact with a cooling medium for the greater portion of its length, thereby providing improved heat transfer and allowing the operation of engines at higher firing pressures and increased thermal loading.
However, conventional wet-type cylinder liners have several disadvantages. Since the wet liner requires substantial space for the cooling liquid, use of such liners substantially increases the distance between the center lines of the several cylinders, this increase being necessary to insure space for cylinder block and liner walls of adequate thickness to withstand the increased mechanical and thermal loads and to resist cavitation erosion. Also this increase is necessary in order to provide room for a flange to support the wet-type liner in the cylinder block. The greater distance between cylinder bores, of course, increases the overall length of the engine, and thereby adds cost, weight and bulkiness to the engine.
Wet liners also require the installation of seals between the lower portion of the liner and the cylinder block to prevent the cooling medium from migrating into the oil and vice-versa. These seals are susceptible to damage and adversely affect engine reliability and durability, and increase maintenance costs.
On the other hand, a fully dry liner, where the liner is separated from the cooling medium throughout its entire length also has several disadvantages. The heat transfer between the liner and the cooling medium is restricted because the coolant flow is disrupted by cast cylinder head screw bosses located around the upper portion of the liner. Also it is difficult and expensive to cast clean cooling passages around the liner supporting structure of the cylinder block. Finally, the dry-type liner has a lesser capacity for heat dissipation from the cylinder than a fully wet-type liner.
Thus, both conventional types of liners, namely the fully wet-type and the fully dry-type, have significant disadvantages.
The present invention provides a hybrid wet/dry cylinder liner which combines the best features of conventional wet cylinder liners and conventional dry cylinder liners. More specifically, the present invention provides a structure in which the upper portion of the liner, where combustion occurs and where therefore heat transfer is most important, is of the wet-type, while the lower portion of the liner, where less heat transfer is needed, is constructed of a dry-type thin wall configuration not requiring any cooling. The present invention allows engines to be constructed with the distance between the cylinder bores the same as that for present day engines with completely dry liners by dividing the liner into two distinctive portions, one wet and one dry. The upper, or wet, portion of the liner is provided with a fully controlled passage around the liner for cooling fluid. At the same time the lower, or dry, portion of the liner is constructed to provide a firm support for the entire liner and also to provide a seat for the liner which eliminates any need for an additional seal between the upper (wet) and lower (dry) portions of the liner and eliminates the need for any additional seal normally required with wet-type liners to preclude mixing of the coolant with the oil of the cylinder.
Accordingly, it is an object of this invention to combine the best features of wet and dry-type liners presently used in high output internal combustion engines, while eliminating the disadvantages of each type of liner.
It is another object of this invention to provide increased cooling in the upper part of the cylinder where firing occurs and where the heat is greatest and reduced cooling in the lower part of the cylinder where the cooling requirements are not as great.
It is a further object of this invention to provide a construction in which the engagement of the lower (dry) portion of the cylinder liner provides effective support for the entire liner and enables the upper (wet) portion of the liner to be made thinner than would otherwise be the case.
It is still another object of this invention to provide a construction in which a shoulder on the liner is brought into sealing engagement with a shoulder on the cylinder wall eliminating the need for a special seal therebetween.